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Module 2

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Susan Miller-Hendrix

on 7 August 2014

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Transcript of Module 2

Common types of physical evidence
Plastic, rubber, and other polymers
Powder residues
Serial numbers
Soils and minerals
Tool marks
Vehicle lights
Wood and other vegetative matter
Identification
The ultimate goal when identifying a specific physical or chemical substance is to exclude other substances
1. Requires repeatable testing procedures that have characteristic results for specific standard materials
2. Require that number and type of tests be:
a. sufficient to exclude all other substances (ex. eliminate all but one substance
Common Types of Evidence
blood, semen, and saliva-identity and possible origin
documents-authenticity and source
drugs
explosives
fibers-transfers establish relationships
fingerprints
firearms and ammunition
Identification
Determination of chemical or physical identity of a substance with as near absolute certainty as possible
Illicit drug preparation-heroine, cocaine, barbiturates
Gasoline residue from debris of a fire
Nature of explosive residues-dynamite and TNT
Species of origin-blood,semen, hair, wood
Identification
Each type of evidence requires a different test; each test has a different degree of specificity
Substance A-has one test
Substance B-maybe has 5 or 6 tests
Forensic Scientists discover at what point analysis is concluded
has be be beyond reasonable doubt for court of law
Module 2 Lesson 1 Part I
The Nature of Evidence

Methods used by forensic science when examining evidence
1. Identification
is the process of determining a substance physical or chemical identity

Methods used by forensic science when examining evidence
2. Comparison
is the process of ascertaining whether two or more objects have a common origin
Locard's Exchange Principle
Every person who is physically involved in a crime leaves some minute trace of his or her presence and often takes something away.
This is Dr. Edmond Locard's Principle of Contact, proposed when he began his forensic laboratory in 1910.
Common Types of Physical Evidence
Glass
Hair
Impressions
Organs and physiological fluids
Paint
Petroleum products
Plastic bags
Comparison
Need to determine which properties to compare from the suspect and the standard/reference specimen
*determining if the two samples are the same
Need to conclude the origin of the speciments
*determining how likely it is that the two samples came from the same source
Comparison
Suspect specimen and a standard/reference specimen run through same tests and examinations to determine common origin
Ex. hair at a crime scene to hairs in suspect's head
Ex. paint chip in victims clothing to car in hit-and-run
Comparison
Procedure:
1. Combinations of select properties chosen from suspect and standard/reference sample
a. Which properties and how many properties depends on type of materials
b. Once testing is complete, forensic scientist conclude on origins of species
c. If one or more properties do not agree-not same origin
d. If all properties degree-always of the same origin
Comparison
Not necessarily always the same
Evidential value-probability of ascertaining origins of two or more specimens
Probability
frequency of occurrence of an event
odds at which a certain event will occur
Class Characteristics
The properties that all members of a certain group of objects have in common
Need a high degree of certainty
Probability is a determining factor
Class
Characteristics
Initial categories are broad and then narrowed as more information is obtained
Example:
green substance
green paint
green car paint
green car paint from Ford Manufacturing Company
Green car paint from ford produced 1998-2000
green car paint from ford produced 1998-2000, used on Mustang or Explorer
Class
Characteristics
The previous paint example was a refined class evidence identification
The paint was identified by comparing its class characteristics with those of known standards or previously established criteria
The paint is considered class evidence
Other Examples
Single layered paint
Soil
Glass fragments too small to fit back together
Hairs
Fibers
Full transcript